Laser welding has many well known advantages over conventional resistance welding. For example, laser welding provides low distortion, small heat affected zones (HAZ), improved mechanical/structural performance, increased speed of processing, improved process controllability/consistency and single sided access. However, one great disadvantage of laser welding is the requirement of tight gaps between the parts to be welded which in turn requires precise positioning of the laser beam relative to the parts to be welded.
Typically, laser welding systems utilize welding clamps which clamp and fix the parts to be welded together. Robots are used to perform the welding operation. A laser beam generator or source generates or produces a laser beam. The laser beam is transmitted to a focusing head via a fiber optic cable. The focusing head is installed or mounted on the end of the robot arm. The robot is then programmed to accurately position the focusing head, and thus the laser beam focal point, relative to the parts to be welded. The welding is done sequentially as the robot must move from weld joint to weld joint. With a robotic-based laser welding system, time is wasted during non-welding motion from joint to joint. Also, accuracy and repeatability of positioning the laser beam focal point relative to the surface of the parts to be welded is difficult to accomplish at high speeds with a robot. Part dimensional variations and motion trajectory errors lead to difficulties in obtaining consistent weld quality.
U.S. Pat. No. 4,654,505 issued Mar. 31, 1987 to Sciaky et al. discloses a multi-point laser welding system for vehicle bodies and the like which includes apparatus for positioning the pieces to be welded, apparatus for gripping the pieces to be welded, and apparatus for welding the positioned and gripped pieces at specific points. The '505 patent employs a laser beam delivery system using multiple motor driven optical mirrors controlled by a computer program to focus a laser beam upon a single point on the parts to be welded. The '505 patent does not disclose moving the laser beam across the parts to be welded to provide a linear or curved stitch, as opposed to a single point spot weld. Additionally, the '505 patent does not disclose the use of a fiber optic cable for transmitting a laser beam from a laser beam source to a focusing head secured to a clamping fixture. Instead, the laser welding system disclosed in the '505 patent employs multiple mirrors to transmit a laser beam from a laser beam source to the pieces or parts to be welded.
The laser welding system disclosed in the '505 patent also does not disclose confining the laser beam within a clamp fixture as the laser beam is used to perform the welding. Instead, the laser beam travels outside of or externally from the fixture used to clamp the pieces to be welded together. Confining the laser beam so that the laser beam is directly transferred from a focusing head to the parts to be welded is critical since exposed laser beams may create hazardous conditions for those workers near the laser welding system.